Power protection glossary

Coaxial protection
Power protection components feature two types of coaxial connection jacks — one specifically designed to handle satellite TV (or DBS) signals, and another for a standard cable/broadcast antenna connection. That's because the amount of voltage that normally occurs between a satellite dish and satellite receiver is much greater than the voltage found in a typical cable TV signal.

Delayed/sequential turn-on
Power protection components with a delayed turn-on feature typically provide one or more outlets that receive current several seconds after the other components have been turned on. For example, you could set your amplifier or receiver to turn on after your other gear to prevent the unwanted "thump" that can damage your speakers.

EMI (Electromagnetic Interference)
This type of interference is caused by an electromagnetic field generated close to your system, often by common household appliances. A washing machine or a vacuum cleaner can add a loud buzzing or a low hum to your audio system or distort your TV picture. You can protect against EMI with a line conditioner.

Ground fault
The shorting of a circuit or an electrical device causing current to flow to any location other than the structure's common grounding electrode. This can be caused by damaged or faulty wiring, or by the installation of a second grounding electrode.

US and Canadian electrical codes require a common grounding electrode for all wires that enter a structure.

Many power protection devices feature built-in ground fault indicators. If a ground fault is detected, we strongly recommend that you consult a licensed electrician as soon as possible to protect your system and your home.

Joules
A unit of energy. One Joule is equal to the work done when a current of one ampere is passed through a resistance of one ohm for one second. A 100-watt light bulb uses 100 Joules every second. In power protection, the higher the Joule rating, the better the surge protection.

Line conditioning
A power protector component with line, or power, conditioning filters power before passing it on to your system. It minimizes or removes EMI and RFI using special conditioning circuitry.

MOV (Metal Oxide Varistor)
MOVs are the core of many power protection components. A varistor is a variable resistor, designed to react to the voltage level of the incoming current and change its resistance accordingly. When incoming power is slightly above the safe level of the component, for example, the MOV drains energy from the current as it passes through, bringing the level back down. During a sudden voltage spike, the influx of power severely damages or destroys the MOV, breaking the connection and helping protect your devices.

Over-voltage
Over-voltage can happen when high-current electrical motors, such as air conditioners, switch off. The extra voltage that results from the sudden decrease in demand is dissipated through the rest of the power line, and can exceed the recommended peak current levels of many electronic components. Over-voltage is sometimes confused with a lightning strike, which is actually a voltage spike.

Power regeneration
Rather than just filtering incoming house current like a line conditioner, a power regenerator takes the incoming current and uses it to create its own power to send on to your system. Incoming alternating current (AC) is converted to direct current (DC), stripping off any electronic noise in the process. The DC is then regenerated back into AC through circuitry that tightly controls the voltage level. This outgoing power has none of the electronic noise or voltage irregularities of the source.

RFI (Radio Frequency Interference)
This type of interference results from radio waves created by radio stations, microwaves, cell phones, lawn mowers, generators, and many other sources. These patterns of interference, these patterns of interference often originate a great distance from your home. They're usually heard as clicks and pops, though sometimes cellphone conversations or nearby radio transmissions can "bleed through" your system's audio. RFI can also appear as "snow" on your TV's picture.

Switched outlet
An AC outlet built into your power protection component or A/V receiver that delivers power only when the component is turned on. Commonly these outlets are used for DVD players, amplifiers and other ancillary components that might not have stored settings.

UL-listed
UL stands for Underwriters Laboratories Inc., an independent, non-profit, product safety testing and certification organization. Since 1894, UL has been one of the leaders in testing products for public safety. If a product is UL-listed, it has been tested and approved by this organization.

Under-voltage
Under-voltage is a temporary decrease in available power throughout your home's electrical system. This decrease can be caused by devices that draw a lot of power when they start up, such as air-conditioning units, compressors, and power tools. It can also occur during times of peak power demand, when electric utility companies lower voltage levels in certain areas for hours or days at a time, particularly during hot weather. Under-voltage can reduce the efficiency and life span of electronic equipment, especially those that use motors like computers, DVD players, and game consoles.

Unswitched outlet
An AC outlet built into your power protection component or A/V receiver that delivers power at all times, as long as the powering component receives power. That means it will deliver power when the connected device is on or in standby mode, and won't when its own fuse or breaker on a power protection component is blown or in the off position. Unswitched outlets are used by equipment with memory or components that use remotes, such as DVRs or televisions.

UPS (Uninterruptible Power Supply)
A power protection component that uses an internal battery to deliver backup power to connected equipment during temporary electrical outages. UPS components are especially useful for home computer networks, because the backup power lets you save necessary data and safely shut down your PC. They're also helpful for saving the personalized settings stored in your home A/V system components. And if you have a rear-projection TV, this backup power can keep the fan running so the bulb cools down properly, preventing damage.

Voltage spike
Voltage spikes are usually caused by a nearby lightning strike. They can also occur when the power is restored after having gone out during a storm. A spike is an instantaneous enormous voltage increase, and can result in catastrophic damage to unprotected electronic components.

Related articles and videos

Crutchfield Writer Biography

Ralph Graves

Ralph Graves is one of Crutchfield's blog editors, and part of the company's social media team. He writes about home audio/video gear, specializing in Apple-related and wireless technologies. Ralph holds a master's degree in music composition, and his works have been released on various labels. He's served as product manager for an independent classical and world music label, produced several recordings, and worked extensively in public broadcasting. Since 1984 he's hosted a weekly classical music program on WTJU, and is also active as a blogger and podcaster.